1. Field of the Invention
The present invention relates to a reusable image recording paper which is used in an image forming apparatus based on an electrophotographic process or a thermal transfer process and more particularly to a reusable image recording paper which withstands repetitions of a cycle consisting of image formation with an image forming material and removal of the image either by use of an image removing apparatus destined for the removal from substrate of the image forming material fixed thereto by an image forming apparatus or by use of an image forming apparatus equipped with such an image removing device.
2. Description of the Related Art
Recently, because of the emergence of the problem of environmental pollution on a global scale, the importance of the protection of forest resources has been recognized with the result that the reduction in the consumption of wood resource as a material for paper has become important. As part of the measure for reducing the consumption, the reuse as waste paper of used paper is advocated instead of disposing it as a waste. Although the reuse of waste paper is an important recovery of resources, reuse of paper involves many problems.
For example, as regards the recovery of waste paper, particularly in business companies, the problems raised include leak of secret documents or data, different recovery operations according to the kinds of paper, transportation of paper and locations and controls of waste paper collecting places. In addition, since repulping treatment of waste paper shortens the pulp fibers, the quality of the regenerated paper tends to become inferior. And, a de-inking apparatus for de-inking treatment of existing images become necessary. Further, since a paper making machine itself is gigantic, complicated and expensive, the paper reuse work is intractable by any individual and is only manageable by a limited number of enterprises.
Unless the above-mentioned discriminate recovery, transportation, collection, operation of gigantic equipment and the like are conducted in an efficient way, a large amount of energy will be consumed (i.e., increase in CO.sub.2 emission) and as a result the problem of global warming phenomenon which is one of global environmental problems and which ensues from the increase in the amount of CO.sub.2 will be exasperated.
As one of the solutions to the above-mentioned problems, there have been proposed methods whereby an image on a sheet of paper once formed is erased so that the paper is used again. Exemplary of these methods are those described in the following laid open patent applications.
Japanese Patent Application Laid-Open (JP-A) No. 2-55195 provides a erasable printing substrate by coating an image support material made, for example, of plastics, metal, liquid-impermeable paper or ceramics, with a silicone sealing agent, i.e., a silicone rubber-based releasing agent. When removing an image, the image printed in a thermally fusible ink on the support is heated and pressed together with a thermally fusible release coating present therebetween and is then cooled down to remove the image from the support.
In this case, since the silicone sealing agent tends to migrate, it adheres to contact surfaces of paper feeder or delivery rollers and the like inside an apparatus to cause paper block up. In addition, the block up causes dust and toner to float inside the apparatus and to deposit on paper, thus smearing the paper. An attempt to form a thin and uniform coating layer of the silicone sealing agent on a substrate to reduce the migration of the silicone sealing agent has proved to be unsuccessful. This is because, where the substrate is simple paper, such factor as penetration of the silicone sealing agent into paper or irregularity on the surface of paper causes discontinuity of coating layer including uncoated areas. Accordingly, in order to fulfill the function as an erasable printing substrate, the film thickness of the silicone sealing agent needs to be at least Sum, which enhances the surface smoothness and results in poor fixability of image.
Besides, in the above-cited invention, utilized as a substrate is a material which is exemplified by polyethylene terephthalate (PET) or a laminated film and which usually has a surface smoothness of at least 300 seconds as measured by a Beck's smoothness meter. In the case where such a substrate is coated with a silicone sealing agent layer having a thickness of 3 um or more which is necessary for satisfactory removal of an thermally fusible ink, the fixability of image recording material is so poor that mere rubbing the image with hand will cause the image part to easily peel, thus resulting in unsatisfactory preservation of the record.
Japanese Patent Application Laid-Open (JP-A) No. 5-216376 provides an erasable printing paper having a recording surface coated with a releasing agent, which, when erasing the image, is press-contacted with a medium comprised of a material causing an easy offset so that the image forming toner will be transferred and removed. The releasing agents utilized include a silicone oil, a fluorinated oil and other aliphatic oils. When these oils are utilized, in order to obtain a satisfactory level of toner release property, it will be necessary to apply them to paper in such a large amount that the coated printing paper will become transparent. Therefore, the problems involved are that the obtained printing paper will present an appearance different from that of plain paper, that mere rubbing the image with hand causes the image part to easily peel due to poor fixability thus resulting in unsatisfactory preservation of the record and that migration tendency of the releasing agent presents the same problems as in the case of Japanese Patent Application Laid-Open (JP-A) No. 2-55195.
Japanese Patent Application Laid-Open (JP-A) No. 6-219068 provides a reusable printing paper obtained by coating or impregnating a thermal transfer recording paper with a thermally modifiable material which, when heated, becomes less adherent to an image forming material and which is exemplified by a fluorine-containing acrylate. In this case, the recording paper is a thermal transfer recording paper, which has a higher smoothness and poor fixability in comparison with plain paper. The above-mentioned thermally modifiable material has poor adhesion to the thermal transfer recording paper as a substrate and exhibits migration, which causes slip between paper delivery rollers and the recording paper thereby increasing the possibility of causing block up of recording paper and failure in setting due to deviation of location. Although there is described a technique consisting of creating on the thermal transfer printing paper a limited region where the thermally modifiable material is not coated or impregnated as a measure for the prevention of the above-mentioned problems, fresh problems will be more labor that will be involved, difficulty in the manufacture of the printing paper and higher production costs.
In addition, in the case of the above-mentioned reusable recording paper utilizing a thermally modifiable material, a fixing treatment by the application of pressure is necessary, which is disadvantageous from the viewpoint of wide use of this type of paper, because, in current copiers based on electrophotography, the fixation of an image forming material on a recording paper is performed by a thermal press. Other problems include that the writings by pencil, ball point pen, water base ink pen and the like are too light-colored to be discernible and that the surface is too repellent to write.